Systems and methods for signaling and interference detection in sensor devices

ABSTRACT

An input device processing system comprises a sensor module that transmits a first transmitter signal with a transmitter electrode and receives a resulting signal with a receiver electrode. The first transmitter signal comprises a first transmitter frequency, and the resulting signal comprises effects corresponding to the first transmitter signal. A demodulation module demodulates the resulting signal to produce a first signal (e.g., an upper sideband signal) and a second signal (a lower sideband signal), selectably determines a first measurement of a change in capacitive coupling between the transmitter electrode and the receiver electrode based on at least one of the first and second signals, and determines positional information for an input object based on the first measurement.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to U.S. Prov. Pat. App. No. 61/383,655,filed Sep. 16, 2010, and U.S. Prov. Pat. App. No. 61/406,437, filed Oct.25, 2010, both of which are incorporated by reference herein.

FIELD OF THE INVENTION

This invention generally relates to electronic devices, and morespecifically relates to sensor devices.

BACKGROUND OF THE INVENTION

Input devices including proximity sensor devices (also commonly calledtouchpads or touch sensor devices) are widely used in a variety ofelectronic systems. A proximity sensor device typically includes asensing region, often demarked by a surface, in which the proximitysensor device determines the presence, location and/or motion of one ormore input objects. Proximity sensor devices may be used to provideinterfaces for the electronic system. For example, proximity sensordevices are often used as input devices for larger computing systems(such as opaque touchpads integrated in, or peripheral to, notebook ordesktop computers).

Proximity sensor devices may typically incorporate either profilecapacitive sensors or capacitive image sensors. Capacitive profilesensors alternate between multiple axes (e.g., x and y), whilecapacitive image sensors scan multiple transmitter rows to produce amore detailed capacitive “image” of “pixels” associated with an inputobject. While capacitive image sensors are advantageous in a number ofrespects, such sensors may be susceptible to various types ofinterference. Accordingly, there is a need for improved sensor systemsand methods for detecting and avoiding various such interference.

BRIEF SUMMARY OF THE INVENTION

A processing system in accordance with one embodiment comprises a sensormodule and a demodulation module. The sensor module comprises sensorcircuitry, the sensor module configured to transmit a first transmittersignal with a transmitter electrode and receive a resulting signal witha receiver electrode, wherein the first transmitter signal comprises afirst transmitter frequency, and the resulting signal comprises effectscorresponding to the first transmitter signal. The demodulation moduleis configured to demodulate the resulting signal to produce an uppersideband signal and a lower sideband signal, selectably determine afirst measurement of a change in capacitive coupling between thetransmitter electrode and the receiver electrode based on at least oneof the upper sideband signal and the lower sideband signal, anddetermine positional information for an input object based on the firstmeasurement.

A method in accordance with one embodiment of the present inventionincludes: transmitting a first transmitter signal with a transmitterelectrode, the first transmitter signal comprising a first transmitterfrequency; receiving a resulting signal with a receiver electrode, theresulting signal comprising effects corresponding to the firsttransmitter signal; demodulating the resulting signal to produce anupper sideband signal and a lower sideband signal; selectablydetermining a first measurement of a change in capacitive couplingbetween the transmitter electrode and the receiver electrode based on atleast one of the upper sideband signal and the lower sideband signal;and determining positional information for an input object based on thefirst measurement.

A capacitive sensor device in accordance with one embodiment of theinvention comprises a transmitter electrode, a receiver electrode, and aprocessing system communicatively coupled to the transmitter electrodeand the receiver electrode. The processing system is configured to:transmit a first transmitter signal with the transmitter electrode, thefirst transmitter signal comprising a first transmitter frequency;receive a resulting signal with the receiver electrode, the resultingsignal comprising effects corresponding to the first transmitter signal;demodulate the resulting signal to produce an upper sideband signal anda lower sideband signal; selectably determine a measurement of a changein capacitive coupling between the transmitter electrode and thereceiver electrode based on at least one of the upper sideband signaland the lower sideband signal; and determine positional information foran input object based on the measurement.

BRIEF DESCRIPTION OF DRAWINGS

The preferred exemplary embodiment of the present invention willhereinafter be described in conjunction with the appended drawings,where like designations denote like elements, and:

FIG. 1 is a block diagram of an exemplary system that includes an inputdevice in accordance with an embodiment of the invention;

FIG. 2 is a block diagram of sensor electrodes in accordance with anexemplary embodiment of the invention;

FIG. 3 is a conceptual block diagram depicting an exemplary embodimentof the invention;

FIG. 4 is a conceptual block diagram depicting an exemplary embodimentof the invention;

FIG. 5A is a schematic diagram of demodulation module circuitry inaccordance with one embodiment of the invention;

FIG. 5B is a schematic diagram of demodulation module circuitry inaccordance with one embodiment of the invention; and

FIG. 6 is a schematic diagram of demodulation module circuitry inaccordance with another embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, brief summary, or the following detailed description.

Various embodiments of the present invention provide input devices andmethods that facilitate improved usability. FIG. 1 is a block diagram ofan exemplary input device 100, in accordance with embodiments of theinvention. The input device 100 may be configured to provide input to anelectronic system (not shown). As used in this document, the term“electronic system” (or “electronic device”) broadly refers to anysystem capable of electronically processing information. Somenon-limiting examples of electronic systems include personal computersof all sizes and shapes, such as desktop computers, laptop computers,netbook computers, tablets, web browsers, e-book readers, and personaldigital assistants (PDAs). Additional example electronic systems includecomposite input devices, such as physical keyboards that include inputdevice 100 and separate joysticks or key switches. Further exampleelectronic systems include peripherals such as data input devices(including remote controls and mice), and data output devices (includingdisplay screens and printers). Other examples include remote terminals,kiosks, and video game machines (e.g., video game consoles, portablegaming devices, and the like). Other examples include communicationdevices (including cellular phones, such as smart phones), and mediadevices (including recorders, editors, and players such as televisions,set-top boxes, music players, digital photo frames, and digitalcameras). Additionally, the electronic system could be a host or a slaveto the input device.

The input device 100 can be implemented as a physical part of theelectronic system, or can be physically separate from the electronicsystem. As appropriate, the input device 100 may communicate with partsof the electronic system using any one or more of the following: buses,networks, and other wired or wireless interconnections. Examples includeI²C, SPI, PS/2, Universal Serial Bus (USB), Bluetooth, RF, and IRDA.

In FIG. 1, the input device 100 is shown as a proximity sensor device(also often referred to as a “touchpad” or a “touch sensor device”)configured to sense input provided by one or more input objects 140 in asensing region 120. Example input objects include fingers and styli, asshown in FIG. 1.

Sensing region 120 encompasses any space above, around, in and/or nearthe input device 100 in which the input device 100 is able to detectuser input (e.g., user input provided by one or more input objects 140).The sizes, shapes, and locations of particular sensing regions may varywidely from embodiment to embodiment. In some embodiments, the sensingregion 120 extends from a surface of the input device 100 in one or moredirections into space until signal-to-noise ratios prevent sufficientlyaccurate object detection. The distance to which this sensing region 120extends in a particular direction, in various embodiments, may be on theorder of less than a millimeter, millimeters, centimeters, or more, andmay vary significantly with the type of sensing technology used and theaccuracy desired. Thus, some embodiments sense input that comprises nocontact with any surfaces of the input device 100, contact with an inputsurface (e.g. a touch surface) of the input device 100, contact with aninput surface of the input device 100 coupled with some amount ofapplied force or pressure, and/or a combination thereof. In variousembodiments, input surfaces may be provided by surfaces of casingswithin which sensor electrodes reside, by face sheets applied over thesensor electrodes or any casings, etc. In some embodiments, the sensingregion 120 has a rectangular shape when projected onto an input surfaceof the input device 100.

The input device 100 may utilize any combination of sensor componentsand sensing technologies to detect user input in the sensing region 120.The input device 100 comprises one or more sensing elements fordetecting user input. As several non-limiting examples, the input device100 may use capacitive, elastive, resistive, inductive, magnetic,acoustic, ultrasonic, and/or optical techniques.

Some implementations are configured to provide images that span one,two, three, or higher dimensional spaces. Some implementations areconfigured to provide projections of input along particular axes orplanes.

In some resistive implementations of the input device 100, a flexibleand conductive first layer is separated by one or more spacer elementsfrom a conductive second layer. During operation, one or more voltagegradients are created across the layers. Pressing the flexible firstlayer may deflect it sufficiently to create electrical contact betweenthe layers, resulting in voltage outputs reflective of the point(s) ofcontact between the layers. These voltage outputs may be used todetermine positional information.

In some inductive implementations of the input device 100, one or moresensing elements pick up loop currents induced by a resonating coil orpair of coils. Some combination of the magnitude, phase, and frequencyof the currents may then be used to determine positional information.

In some capacitive implementations of the input device 100, voltage orcurrent is applied to create an electric field. Nearby input objectscause changes in the electric field, and produce detectable changes incapacitive coupling that may be detected as changes in voltage, current,or the like.

Some capacitive implementations utilize arrays or other regular orirregular patterns of capacitive sensing elements to create electricfields. In some capacitive implementations, separate sensing elementsmay be ohmically shorted together to form larger sensor electrodes. Somecapacitive implementations utilize resistive sheets, which may beuniformly resistive.

Some capacitive implementations utilize “self capacitance” (or “absolutecapacitance”) sensing methods based on changes in the capacitivecoupling between sensor electrodes and an input object. In variousembodiments, an input object near the sensor electrodes alters theelectric field near the sensor electrodes, thus changing the measuredcapacitive coupling. In one implementation, an absolute capacitancesensing method operates by modulating sensor electrodes with respect toa reference voltage (e.g. system ground), and by detecting thecapacitive coupling between the sensor electrodes and input objects.

Some capacitive implementations utilize “mutual capacitance” (or“transcapacitance”) sensing methods based on changes in the capacitivecoupling between sensor electrodes. In various embodiments, an inputobject near the sensor electrodes alters the electric field between thesensor electrodes, thus changing the measured capacitive coupling. Inone implementation, a transcapacitive sensing method operates bydetecting the capacitive coupling between one or more transmitter sensorelectrodes (also “transmitter electrodes” or “transmitters”) and one ormore receiver sensor electrodes (also “receiver electrodes” or“receivers”). Transmitter sensor electrodes may be modulated relative toa reference voltage (e.g., system ground) to transmit transmittersignals. Receiver sensor electrodes may be held substantially constantrelative to the reference voltage to facilitate receipt of resultingsignals. A resulting signal may comprise effect(s) corresponding to oneor more transmitter signals, and/or to one or more sources ofenvironmental interference (e.g. other electromagnetic signals). Sensorelectrodes may be dedicated transmitters or receivers, or may beconfigured to both transmit and receive.

In this regard, FIG. 2 illustrates, conceptually, an exemplary set ofcapacitive sensor electrodes 200 configured to sense in a sensingregion. For clarity of illustration and description, FIG. 2 shows apattern of simple rectangles; however, it will be appreciated that theinvention is not so limited, and that a variety of electrode patternsmay be suitable in any particular embodiment. In one embodiment, sensorelectrodes 210 are configured as receiver electrodes and sensorelectrodes 220 are configured as transmitter electrodes. In otherembodiments, sensor electrodes 210 are configured to sense input objectposition and/or motion in the X direction and sensor electrodes 220 areconfigured to sense input object position and/or motion in the Ydirection.

Sensor electrodes 210 and 220 are typically ohmically isolated from eachother. That is, one or more insulators separate sensor electrodes 210and 220 and prevent them from electrically shorting to each other. Insome embodiments, sensor electrodes 210 and 220 are separated byinsulative material disposed between them at cross-over areas; in suchconstructions, the sensor electrodes 210 and/or sensor electrodes 220may be formed with jumpers connecting different portions of the sameelectrode. In some embodiments, sensor electrodes 210 and 220 areseparated by one or more layers of insulative material. In some otherembodiments, sensor electrodes 210 and 220 are separated by one or moresubstrates; for example, they may be disposed on opposite sides of thesame substrate, or on different substrates that are laminated together.The capacitive coupling between the transmitter electrodes and receiverelectrodes change with the proximity and motion of input objects in thesensing region associated with the transmitter electrodes and receiverelectrodes.

In some embodiments, the sensor pattern is “scanned” to determine thesecapacitive couplings. That is, the transmitter electrodes are driven totransmit transmitter signals. Transmitters may be operated such that onetransmitter electrode transmits at one time, or multiple transmitterelectrodes transmit at the same time. Where multiple transmitterelectrodes transmit simultaneously, these multiple transmitterelectrodes may transmit the same transmitter signal and effectivelyproduce an effectively larger transmitter electrode, or these multipletransmitter electrodes may transmit different transmitter signals. Forexample, as described in further detail below, multiple transmitterelectrodes may transmit different transmitter signals according to oneor more coding schemes that enable their combined effects on theresulting signals of receiver electrodes to be independently determined.

The receiver sensor electrodes may be operated singly or multiply toacquire resulting signals. The resulting signals may be used todetermine measurements of the capacitive couplings. A set of measuredvalues from the capacitive pixels form a “capacitive image” (also“capacitive frame”) representative of the capacitive couplings at thepixels. Multiple capacitive images may be acquired over multiple timeperiods, and differences between them used to derive information aboutinput in the sensing region. For example, successive capacitive imagesacquired over successive periods of time can be used to track themotion(s) of one or more input objects entering, exiting, and within thesensing region.

Referring again to FIG. 1, a processing system 110 is shown as part ofthe input device 100. The processing system 110 is configured to operatethe hardware of the input device 100 (including, for example, thevarious sensor electrodes 200 of FIG. 2) to detect input in the sensingregion 120. The processing system 110 comprises parts of or all of oneor more integrated circuits (ICs) and/or other circuitry components. Forexample, as described in further detail below, a processing system for amutual capacitance sensor device may comprise transmitter circuitryconfigured to transmit signals with transmitter sensor electrodes,and/or receiver circuitry configured to receive signals with receiversensor electrodes).

In some embodiments, the processing system 110 also compriseselectronically-readable instructions, such as firmware code, softwarecode, and/or the like. In some embodiments, components composing theprocessing system 110 are located together, such as near sensingelement(s) of the input device 100. In other embodiments, components ofprocessing system 110 are physically separate with one or morecomponents close to sensing element(s) of input device 100, and one ormore components elsewhere. For example, the input device 100 may be aperipheral coupled to a desktop computer, and the processing system 110may comprise software configured to run on a central processing unit ofthe desktop computer and one or more ICs (perhaps with associatedfirmware) separate from the central processing unit. As another example,the input device 100 may be physically integrated in a phone, and theprocessing system 110 may comprise circuits and firmware that are partof a main processor of the phone. In some embodiments, the processingsystem 110 is dedicated to implementing the input device 100. In otherembodiments, the processing system 110 also performs other functions,such as operating display screens, driving haptic actuators, etc.

The processing system 110 may be implemented as a set of modules thathandle different functions of the processing system 110. Each module maycomprise circuitry that is a part of the processing system 110,firmware, software, or a combination thereof. In various embodiments,different combinations of modules may be used. Example modules includehardware operation modules for operating hardware such as sensorelectrodes and display screens, data processing modules for processingdata such as sensor signals and positional information, and reportingmodules for reporting information. Further example modules includesensor operation modules configured to operate sensing element(s) todetect input, identification modules configured to identify gesturessuch as mode changing gestures, and mode changing modules for changingoperation modes.

In some embodiments, the processing system 110 responds to user input(or lack of user input) in the sensing region 120 directly by causingone or more actions. Example actions include changing operation modes,as well as GUI actions such as cursor movement, selection, menunavigation, and other functions. In some embodiments, the processingsystem 110 provides information about the input (or lack of input) tosome part of the electronic system (e.g. to a central processing systemof the electronic system that is separate from the processing system110, if such a separate central processing system exists). In someembodiments, some part of the electronic system processes informationreceived from the processing system 110 to act on user input, such as tofacilitate a full range of actions, including mode changing actions andGUI actions.

For example, in some embodiments, the processing system 110 operates thesensing element(s) of the input device 100 to produce electrical signalsindicative of input (or lack of input) in the sensing region 120. Theprocessing system 110 may perform any appropriate amount of processingon the electrical signals in producing the information provided to theelectronic system. For example, the processing system 110 may digitizeanalog electrical signals obtained from the sensor electrodes. Asanother example, the processing system 110 may perform filtering orother signal conditioning. As yet another example, the processing system110 may subtract or otherwise account for a baseline, such that theinformation reflects a difference between the electrical signals and thebaseline. As yet further examples, the processing system 110 maydetermine positional information, recognize inputs as commands,recognize handwriting, and the like. In one embodiment, processingsystem 110 includes a determination module configured to determinepositional information for an input device based on the measurement.

“Positional information” as used herein broadly encompasses absoluteposition, relative position, velocity, acceleration, and other types ofspatial information. Exemplary “zero-dimensional” positional informationincludes near/far or contact/no contact information. Exemplary“one-dimensional” positional information includes positions along anaxis. Exemplary “two-dimensional” positional information includesmotions in a plane. Exemplary “three-dimensional” positional informationincludes instantaneous or average velocities in space. Further examplesinclude other representations of spatial information. Historical dataregarding one or more types of positional information may also bedetermined and/or stored, including, for example, historical data thattracks position, motion, or instantaneous velocity over time.

In some embodiments, the input device 100 is implemented with additionalinput components that are operated by the processing system 110 or bysome other processing system. These additional input components mayprovide redundant functionality for input in the sensing region 120, orsome other functionality. FIG. 1 shows buttons 130 near the sensingregion 120 that can be used to facilitate selection of items using theinput device 100. Other types of additional input components includesliders, balls, wheels, switches, and the like. Conversely, in someembodiments, the input device 100 may be implemented with no other inputcomponents.

In some embodiments, the input device 100 comprises a touch screeninterface, and the sensing region 120 overlaps at least part of anactive area of a display screen. For example, the input device 100 maycomprise substantially transparent sensor electrodes overlaying thedisplay screen and provide a touch screen interface for the associatedelectronic system. The display screen may be any type of dynamic displaycapable of displaying a visual interface to a user, and may include anytype of light emitting diode (LED), organic LED (OLED), cathode ray tube(CRT), liquid crystal display (LCD), plasma, electroluminescence (EL),or other display technology. The input device 100 and the display screenmay share physical elements. For example, some embodiments may utilizesome of the same electrical components for displaying and sensing. Asanother example, the display screen may be operated in part or in totalby the processing system 110.

It should be understood that while many embodiments of the invention aredescribed in the context of a fully functioning apparatus, themechanisms of the present invention are capable of being distributed asa program product (e.g., software) in a variety of forms. For example,the mechanisms of the present invention may be implemented anddistributed as a software program on information bearing media that arereadable by electronic processors (e.g., non-transitorycomputer-readable and/or recordable/writable information bearing mediareadable by the processing system 110). Additionally, the embodiments ofthe present invention apply equally regardless of the particular type ofmedium used to carry out the distribution. Examples of non-transitory,electronically readable media include various discs, memory sticks,memory cards, memory modules, and the like. Electronically readablemedia may be based on flash, optical, magnetic, holographic, or anyother storage technology.

Referring now to the conceptual block diagram depicted in FIG. 3, oneembodiment of an exemplary processing system 110 as shown in FIG. 1 mayinclude a system 300. System 300, as illustrated, generally includessensor module 310 communicatively coupled via a set of sensor electrodes(or simply “electrodes”) 304, to demodulation module 320. SensorElectrodes 304 include one or more transmitter electrodes 303 and one ormore receiver electrodes 305. In one embodiment, for example,transmitter electrodes 303 and receiver electrodes 305 are implementedas described above in connection with FIG. 2.

Sensor module 310 includes any combination of hardware and/or softwareconfigured to transmit transmitter signals with transmitter electrodes303 and receive one or more resulting signals with receiver electrodes305. The transmitter signals may comprise any one of a sinusoidalwaveform, square waveform, triangular waveform, sawtooth waveform or thelike. In one embodiment, the frequency of each transmitter signalcomprises a transmitter frequency (f_(ts)), and the resulting signal 316comprises effects corresponding to the first transmitter signal.

In the illustrated embodiment, demodulation module 320 includes anycombination of hardware and/or software (illustrated generally as block322) configured to demodulate the resulting signal 316 to produce signal325 and signal 327. In various embodiments, signal 325 is an uppersideband signal (USB signal) and signal 327 is a lower sideband signal(LSB signal). In another embodiment, signal 325 is a first output signaland signal 327 is a second output signal. Demodulation module is furtherconfigured to selectably determine a measurement of a change incapacitive coupling between a transmitter electrode of transmitterelectrodes 303 and a receiver electrode of receiver electrodes 305 basedon at least one of signal 325 and signal 327. In one embodiment,demodulation module is further configured to selectably determine afirst measurement of a change in capacitive coupling between atransmitter electrode of transmitter electrodes 303 and the receiverelectrode 305 based on at least one of a USB signal and a LSB signal. Inanother embodiment, demodulation module is further configured todetermine a first measurement of a change in capacitive coupling betweena transmitter electrode of transmitter electrodes 303 and a receiverelectrode of receiver electrodes 305 based on a first output signal or asecond output signal. Demodulation module 320 is configured to thendetermine positional information for an input object (e.g., input object140 in FIG. 1) based on the first measurement.

In various embodiments, the measurement of change in capacitive couplingis determined based on one of the signals (e.g., signal 325 or signal327), while a measure of interference is determined based on the othersignal. The interference may include internal and external interferencesources, such as, but not limited to, power supplies, display devices,light sources, electronic components, thermal, etc. In other embodimentsthe first measurement is determined based on the first output signal,while a measure of interference is determined based on the second outputsignal For example, in one embodiment, the measure of interference isdetermined based on a lower sideband signal when the first measurementis determined based on the upper sideband signal, and the measure ofinterference is determined based on an upper sideband signal when thefirst measurement is determined based on lower sideband signal. Invarious embodiments, the measure of interference may be based on a peakto peak amplitude measurement, frequency or bandwidth measurement, powerspectral density measurement, volts squared per hertz or the like.

In accordance with one embodiment, sensor module 310 is configured totransmit a second transmitter signal, different from the firsttransmitter signal, based on the measure of interference. That is,sensor module 310 may selectably transmit a particular transmittersignal when the measure of interference meets some predeterminedcriterion. For example, in one embodiment, sensor module 310 maytransmit the second transmitter signal when it determines that theamplitude of the measure of interference is below a predeterminedthreshold. In another embodiment, sensor module 310 may transmit thesecond transmitter signal when it determines that the amplitude of themeasure of interference is below or meets a predetermined threshold. Inyet other embodiments, sensor module 310 may shift from transmitting thefirst or second transmitter signal to transmitting a third transmittersignal based on a measure of interference of at least one of signal 325or signal 327. In one embodiment, sensor module 310 may transmit a thirdtransmitter signal based on a measure of interference of both signal 325and signal 327. In one embodiment, if any AC information is found to bein the signal used to determine the measurement (either signal 325 orsignal 327), then it can be determined that the signal (at thatfrequency) has interferers. However, if a transmitter signal is found tohave substantially only DC output with no significant AC information,that transmitter signal can be determined to be substantially “clean”.In a further embodiment, if a transmitter signal is found to havesubstantially no DC output with no significant AC information, thattransmitter signal can be determined to be substantially “clean”.

In one embodiment, demodulation module 320 is configured to demodulateresulting signal 316 to produce upper sideband signal 325 and lowersideband signal 327 by mixing resulting signal 316 with a harmonicrejection mixer. That is, block 322 may comprise a harmonic rejectionmixer comprising any suitable combination of hardware and softwarecapable of inserting nulls at harmonic frequencies to suppress unwantedresponses. As will be described in more detail below, in variousembodiments, a harmonic rejection mixer comprises a multi-level mixingsignal. Block 322 may implement a variety of other methods for producingsignal 325 and 327, including without limitation Weaver modulation,Hartley modulation, Bandpass filtering, image reject filtering and thelike.

FIG. 4 is a schematic diagram of exemplary demodulation module circuitry(or simply “circuitry”) 400 suitable for use in block 322 ofdemodulation module 320 of the embodiment depicted in FIG. 3. As shown,demodulation module 420 is configured to demodulate resulting signal 316by mixing resulting signal 316 with two mixing stages (mixing stage 430and mixing stage 440) to produce two outputs: signal 425 and signal 427.In one embodiment, signal 425 may be referred to as first output signaland signal 427 may be referred to as second output signal. In otherembodiments, signal 425 may be referred to as an upper side-band (USB)signal and signal 427 may be referred to as a lower side-band (LSB)signal. Mixing stage 430 comprises a first mixing frequency 431 and asecond mixing frequency 432 corresponding to respective mixers 451 and452. Similarly, mixing stage 440 comprises a third mixing frequency 441and a fourth mixing frequency 442 corresponding to respective mixers 461and 462. Demodulation module 420 is configured to determine ameasurement of a change of capacitive coupling between a transmitterelectrode of transmitter electrodes 303 and a receiver electrode ofreceiver electrodes 305 based on at least one of signal 425 and 427. Invarious embodiments, demodulation module 420 is configured to determinea first measurement of a change of capacitive coupling between atransmitter electrode of transmitter electrodes 303 and a receiverelectrode of receiver electrodes 305 based on at least one of a USBsignal and a LSB signal. In some embodiments, demodulation module 420 isconfigured to determine a first measurement of a change of capacitivecoupling between a transmitter electrode of transmitter electrodes 303and a receiver electrode of receiver electrodes 305 based on a firstoutput signal. Further, demodulation module 420 may be configured todetermine positional information for an input object based on the firstmeasurement.

In accordance with one embodiment, the third mixing frequency 441corresponds to both the first mixing frequency 431 and the firsttransmitter frequency. In the illustrated embodiment, mixing stages 430and 440 are implemented in series; however, the invention is not solimited. In a further embodiment, as described in further detail below,the third mixing frequency 441 is a combination of the first mixingfrequency 431 and the first transmitter frequency such that the thirdmixing frequency 441 corresponds to the absolute value of the differencebetween the first mixing frequency 431 and the first transmitter signal.

In one embodiment, the fourth mixing frequency 442 is in quadrature withthe third mixing frequency 441, and the second mixing frequency 432 isin quadrature with the first mixing frequency 431. That is, first mixingfrequency 431 is 90 degrees out of phase with respect to second mixingfrequency 432, and third mixing frequency 441 is 90 degrees out of phasewith respect to fourth mixing frequency 442.

In one embodiment, while signal 425 is used to determine the firstmeasurement of a change of capacitive coupling between a transmitterelectrode of transmitter electrodes 303 and a receiver electrode ofreceiver electrodes 305, a measure of interference is determined basedon signal 427. This measure of interference may be used for a variety ofpurposes. For example, sensor module 310 may be configured to transmit asecond transmitter signal, different from the first transmitter signal,based on this measure of interference. In this regard, sensor module 310may have any number of candidate transmitter signals having a variety offrequencies and phases. In one embodiment, when sensor module 310transmits a second transmitter signal, different from the firsttransmitter signal, based on the measure of interference, sensor module310 does not continue to transmit the first transmitter signal. Invarious embodiments, the interference of a third transmitter signal maybe determined changing the first mixing frequency and correspondinglythe third mixing frequency. For example, the first mixing frequency maybe increased or decreased such that the difference between thetransmitter signal frequency and the third mixing signal stayssubstantially constant. In such embodiments, the frequency of thetransmitted transmitter signal does not substantially change; however,the interference of a third transmitter signal can be measured.

FIG. 5A is a schematic diagram of exemplary demodulation modulecircuitry (or simply “circuitry”) 500 suitable for use in block 322 ofdemodulation module 320 of the embodiment depicted in FIG. 3. In such anembodiment, signal 525 and signal 527 of FIG. 5A suitably correspond tosignal 325 and signal 327 of FIG. 3. Furthermore, circuitry 500 issuitable for use as one implementation of mixing stages 430 and 440 ofFIG. 4. In such an embodiment, signal 525 and signal 527 of FIG. 5Asuitably correspond to signal 425 and signal 427. In one embodimentsignal 525 may be referred to as USB signal and signal 527 may bereferred to as LSB signal. In other embodiments, signal 525 and signal527 may be referred to as first and second output signals. In thisregard, it will be appreciated that FIG. 5A provides a simplifiedschematic, and that practical embodiments may include additional circuitcomponents. For example, additional filters and mixers may beincorporated into circuitry 500, and/or the illustrated circuitcomponents may be arranged in a variety of topologies.

In the illustrated embodiment, signal 525 and signal 527 are produced bymixing resulting signal 316 with two mixing stages: mixing stage 530(the “first” mixing stage) and mixing stage 540 (the “second” mixingstage). Mixing stage 530 comprises a first mixing frequency 531 and asecond mixing frequency 532 corresponding to respective mixers 581 and582. Similarly, mixing stage 540 comprises a third mixing frequency 541and a fourth mixing frequency 542 corresponding to respective mixers 591and 592. In accordance with one embodiment, the third mixing frequency541 corresponds to the first mixing frequency 531 and the firsttransmitter frequency 532. In various embodiments, mixing frequencies541 and 542 of second stage 540 are a function of one or more of themixing frequencies 531 and 532 of first mixing stage 530 and the firsttransmitter frequency. In one embodiment, for example, the third mixingfrequency 541 corresponds to the absolute value of the differencebetween the first mixing frequency 531 and the first transmitterfrequency, and fourth mixing frequency 542 is in quadrature with thirdmixing frequency 541. The various illustrated mixing frequencies 531,532, 541, and 542 may be sinusoidal, square, triangular, or any othersuitable wave shape, including a three-level (or more) waveform, asdescribed in further detail below.

In one embodiment, the second mixing frequency 532 is in quadrature withthe first mixing frequency 531. Thus, mixing frequency 531 is designatedas f_(c), and mixing frequency is designated as f_(c)′, indicating thatthe two signals are in quadrature with each other. Similarly, fourthmixing frequency 542 (f_(i)′) is in quadrature with the third mixingfrequency 541 (f_(i)). As shown, each output of mixing stage 540 isultimately summed with the inverse of the other output. This summationproduces at least one signal that can be used in determining a measureof the capacitive coupling between transmitter and receiver electrodes.In one embodiment, at least one of the signals produced by the summationis an uncorrelated signal (i.e., a signal with no DC component).

In various embodiments, the measurement of a change of capacitivecoupling may be determined using either signal 525 or signal 527. Insome embodiments, signal 525 and signal 527 may be referred to as USBand LSB signals. In one embodiment, for example, the first measurementis determined based on signal 525 when the transmitter signal frequency(of sensor module 310 in FIG. 3) is greater than the first mixingfrequency 531 (i.e., f_(c)<f_(ts)). In such an embodiment, signal 525may be referred to as an USB signal. In another embodiment, the firstmeasurement is determined based on signal 527 when the transmittersignal frequency (of sensor module 310 in FIG. 3) is less than the firstmixing frequency 531 (i.e., f_(ts)<f_(c)). In such an embodiment, signal527 may be referred to as a LSB.

In various embodiments, circuitry 500 includes one or more filterstages. In the illustrated embodiment, for example, circuitry 500includes a filter stage 570 and a filter stage 580. Filter stage 570includes filters 551 and 552, while filter stage 580 includes filters561 and 562. As shown, filter stage 570 is coupled to first mixing stage530, and filter stage 580 is coupled to second mixing stage 540 via thesummation stage 590. While filter stage 580 is illustrated as followingsummation stage 590, in various embodiments, filter stage 580 may occurbetween second mixing stage 540 and summation stage 590. In oneembodiment, when filter stage follows summation stage 590, filter 561and 562 may be configured to perform signal processing, such asintegration, analog to digital conversion or the like. In variousembodiments, filter stage 570 and 580 may comprise a variety of filtertypes including low pass filters, band pass filters or the like.

In this way, it can be seen that in one embodiment, resulting signal 316of FIG. 5A is first mixed in mixing stage 530 against sine and cosineversions of a carrier frequency (f_(c)), yielding sine and cosineversions of the offset frequency. The resulting signals (from mixingstage 530) may then be low-pass filtered by filter stage 570 to removemixing components that are significantly above the desired quadratureproducts. The second set of mixers of mixing stage 540 operate on thesesignals based on the sine and cosine of the modulation frequency(f_(i)), producing (through filter stage 580) an output 525 and anoutput 527 in a band centered at the modulation offset frequency, suchthat one of the sidebands (output 525 or output 527) is centered at DC.

In the embodiment of FIG. 5B, an alternative to the embodiment of FIG.5A is shown. In such an embodiment, first filter stage 570 is coupled tofirst mixing stage 530. A variety of filter types may be incorporatedinto first filter stage 570. In one embodiment, one or more of thefilters in filter stage 570 are image reject filters. The image rejectfilter may comprise a complex filter, an asymmetric polyphase filter, areal filter or the like. Filter stage 570 may be configured tosubstantially attenuate predetermined frequencies, while notsubstantially attenuating other frequencies. For example, filter 551 maybe configured to attenuate a first frequency, passing through a secondfrequency while filter 552 may be configured to attenuate the secondfrequency while passing through the first frequency. In one embodiment,the first frequency may be a positive frequency and the second frequencymay be a negative frequency. In other embodiments, filter 551 and 552may pass and attenuate unrelated frequencies. Further, filter 551 andfilter 552 may be dynamically configured to attenuate and pass differentfrequency. In one embodiment, filter 551 and filter 552 are dynamicallyconfigured to attenuate and pass different frequency based on therelationship between the transmitter signal frequency and the firstmixer frequency.

As shown in FIG. 5B, in various embodiments, when first filter stage 570comprises at least one image reject filter, a summation stage may not beincluded. As such, the signals 528 and 529 correspond to signals 525 and527, and perform similarly. As is known in the art, a complex filter is“complex” in the sense that it is not a “real” filter—e.g., there is nocomplex conjugate symmetry of the poles in its pole zero map. A complexfilter is also not symmetrical around DC, and is able to segregatepositive frequencies from negative frequencies. In most cases, a complexfilter has two inputs that are already in quadrature, and two outputsthat are in quadrature. Like a complex filter, an asymmetric polyphasefilter may be configured to substantially attenuate predeterminedfrequencies, however an asymmetric polyphase filter takes a single inputand produces two outputs that are 90 degrees apart (an I and Q).

In various embodiments, first filter stage 570 may comprise a singlefilter. In such embodiments, the filter may be configured to attenuateand pass frequencies based on the relationship between the transmittersignal frequency and the first mixer frequency. In one embodiment, thefilter is dynamically configured to attenuate and pass differentfrequency based on the relationship between the transmitter signalfrequency and the first mixer frequency. For example, when thetransmitter signal frequency is less than the first mixer frequency, thefilter may be configured to perform in a lower sideband mode and whenthe transmitter signal frequency is greater than the first mixerfrequency, the filter may be configured to perform in an upper sidebandmode.

Referring now to FIG. 6, in an alternate embodiment, the demodulationmodule includes circuitry 600 configured to demodulate a resultingsignal to produce a quadrature signal 625 and quadrature signal 627,where quadrature signal 625 is in quadrature with signal 525 andquadrature signal 627 is in quadrature with signal 527. In oneembodiment, quadrature signal 625 corresponds to an upper sidebandquadrature signal and quadrature signal 627 corresponds to a lowersideband quadrature signal, when signal 525 corresponds to USB signaland signal 527 corresponds to LSB signal. In other embodiments,quadrature signal 625 corresponds to a first quadrature signal andquadrature signal 627 corresponds to a second quadrature signal, whensignal 525 corresponds to a first output signal and when signal 527corresponds to a second output signal. That is, with respect tocircuitry 500 of FIG. 5A, circuitry 600 includes an additional, thirdmixing stage 690 that comprises a fifth mixing frequency 641 (f_(i)′)and a sixth mixing frequency 642 (f_(i)) corresponding to respectivemixers 641 and 642. In accordance with this embodiment, demodulationmodules 320 and 420 are further configured to determine interference viaone or more of the quadrature signal 625 and quadrature signal 627.

Filters 661 and 662 may be any filter as discussed with reference toFIG. 5A above. Further, as was discussed with reference to FIG. 5A,second filter stage 580 of FIG. 6 may precede summation stage 590 ofFIG. 6. In one embodiment, filter stage 680 precedes summation stage670. In various embodiments, as discussed above with reference to FIG.5B, first filter stage 570 comprises image reject filters (or filter).In such embodiments, with reference to the above discussion related toFIG. 5B summation stage 590 and the summation stage 670 may not beincluded.

Referring again to FIG. 5A, in accordance with one embodiment,demodulation module 520 is configured to simultaneously determine afirst measurement of the change in capacitive coupling between atransmitter electrode of transmitter electrodes 303 and a receiverelectrode of receiver electrodes 305 based on signal 525, and determinea second measurement of the change in the capacitive coupling based onsignal 527. In such an embodiment, the transmitter signal frequencycorresponds to the first mixing frequency and third mixing frequency.Further, the transmitter signal may be described as comprising twofrequencies components, where a first frequency component mixes tosignal 525 and a second frequency component mixes to signal 527. Inother embodiments, the frequency components of the transmitter signalmix to an USB signal and to a LSB signal. The measurements may then beused by processing system 110 to determine positional information for aninput object. Because two different measurements are available, thesystem may determine the positional information based on whicheversignal is substantially “clean” of interference. The interference ineach signal can be determined using any known method. In one embodiment,the two signals can be compared to each other to determine thesubstantially “clean” signal. In further embodiments, the signals can becompared to a baseline value or values to determine the substantially“clean” signal. In one embodiment, if both the upper side-band and lowerside-band signals are determined to comprise interference, either thecarrier signal frequency or the modulation signal frequency may beshifted. In another embodiment, if both the signals are determined tocomprise interference, both the carrier signal frequency and themodulation signal frequency may be shifted.

Mixing signals, such as those illustrated in FIGS. 5A, 5B, and 6, maytake a variety of forms. For example, a particular mixing signal may bea square waveform, a sinusoidal waveform, a triangular waveform, asawtooth waveform or the like. In one embodiment, one or more mixingsignals have a multi-level square waveform. Such a mixer may be referredto as a type of harmonic rejection mixer. A three-level mixer waveformmay substantially suppress any effects due to a third harmonic. In otherembodiments, the mixing signal is not limited to having three levels andmay exhibit more than three levels. In one embodiment, a five-levelmixer waveform may be used to substantially suppress any effects due tothird and fifth harmonics of the transmitter signal. In otherembodiments, further multi-level mixing waveforms may be used tosubstantially suppress further harmonics of the transmitter signal.Multi-level mixing waveforms may reduce harmonic sensitivities of thedemodulation module 320. Furthermore, the illustrated mixers may becombined—e.g., by combining two mixers in a single lowimpedance-to-differential stage folded to two mixing commutators.

Thus, the embodiments and examples set forth herein were presented inorder to best explain the present invention and its particularapplication and to thereby enable those skilled in the art to make anduse the invention. However, those skilled in the art will recognize thatthe foregoing description and examples have been presented for thepurposes of illustration and example only. The description as set forthis not intended to be exhaustive or to limit the invention to theprecise form disclosed.

1. A processing system for an input device, the processing systemcomprising: a sensor module comprising sensor circuitry, the sensormodule configured to transmit a first transmitter signal with atransmitter electrode and receive a resulting signal with a receiverelectrode, wherein the first transmitter signal comprises a firsttransmitter frequency, and the resulting signal comprises effectscorresponding to the first transmitter signal; and a demodulation moduleconfigured to demodulate the resulting signal to produce an uppersideband signal and a lower sideband signal, selectably determine afirst measurement of a change in capacitive coupling between thetransmitter electrode and the receiver electrode based on at least oneof the upper sideband signal and the lower sideband signal, anddetermine positional information for an input object based on the firstmeasurement.
 2. The processing system of claim 1, wherein a measure ofinterference is determined based on the lower sideband signal when thefirst measurement is determined based on the upper sideband signal, andwherein the measure of interference is determined based on the uppersideband signal when the first measurement is determined based on thelower sideband signal.
 3. The processing system of claim 2, wherein thesensor module is configured to transmit a second transmitter signal,different from the first transmitter signal, based on the measure ofinterference.
 4. The processing system of claim 1, wherein thedemodulation module is configured to demodulate the resulting signal toproduce the upper sideband signal and the lower sideband signal bymixing the resulting signal with a harmonic rejection mixer.
 5. Theprocessing system of claim 1, wherein the demodulation module isconfigured to demodulate the resulting signal to produce the uppersideband signal and the lower sideband signal by mixing the resultingsignal with a first mixing stage and a second mixing stage; wherein thefirst mixing stage comprises a first mixing frequency and a secondmixing frequency, the second mixing stage comprises a third mixingfrequency and a fourth mixing frequency, and wherein the third mixingfrequency corresponds to the first mixing frequency and the firsttransmitter frequency.
 6. The processing system of claim 5, wherein thesecond mixing frequency is in quadrature with the first mixingfrequency, and the fourth mixing frequency is in quadrature with thethird mixing frequency.
 7. The processing system of claim 5, wherein thefirst measurement is determined based on the upper sideband signal whenthe transmitter signal frequency is greater than the first mixingfrequency.
 8. The processing system of claim 5, wherein the third mixingfrequency corresponds to the absolute value of the difference betweenthe first mixing frequency and the first transmitter frequency.
 9. Theprocessing system of claim 5, wherein the demodulation module isconfigured to demodulate the resulting signal to produce the uppersideband signal and the lower sideband signal by filtering the resultingsignal with a first filter stage coupled to the first mixing stage and asecond filter stage coupled to the second mixing stage.
 10. Theprocessing system of claim 9, wherein the first filter stage comprisesan image reject filter.
 11. The processing system of claim 5, whereinthe demodulation module is further configured to demodulate theresulting signal to produce an upper sideband quadrature signal and alower sideband quadrature signal, wherein the upper sideband quadraturesignal is in quadrature with the upper sideband signal, and the lowersideband quadrature signal is in quadrature with the lower sidebandsignal and wherein the demodulation module is further configured todetermine interference of the upper sideband quadrature signal andinterference of the lower sideband quadrature signal.
 12. The processingsystem of claim 1, wherein the demodulation module is configured toselectably determine the first measurement of the change in capacitivecoupling between the transmitter electrode and the receiver electrodebased on the at least one of the upper sideband signal and the lowersideband band signal by: determining the first measurement of the changein capacitive coupling between the transmitter electrode and thereceiver electrode based on the upper sideband signal; and determining asecond measurement of the change in the capacitive coupling between thetransmitter electrode and the receive electrode based on the lower sideband signal; wherein the first measurement and the second measurementare determined substantially simultaneously.
 13. A method of capacitivesensing, the method comprising: transmitting a first transmitter signalwith a transmitter electrode, the first transmitter signal comprising afirst transmitter frequency; receiving a resulting signal with areceiver electrode, the resulting signal comprising effectscorresponding to the first transmitter signal; demodulating theresulting signal to produce an upper sideband signal and a lowersideband signal; selectably determining a first measurement of a changein capacitive coupling between the transmitter electrode and thereceiver electrode based on at least one of the upper sideband signaland the lower sideband signal; and determining positional informationfor an input object based on the first measurement.
 14. The method ofclaim 13, wherein a measure of interference is based on the lowersideband signal when the first measurement is determined based on theupper sideband signal, and wherein the measure of interference isdetermined based on the upper sideband signal when the first measurementis determined based on the lower sideband signal.
 15. The method ofclaim 14, further including transmitting a second transmitter signal,different from the first transmitter signal, based on the measure ofinterference.
 16. The method of claim 13, wherein demodulating theresulting signal to produce the upper sideband signal and the lowersideband signal comprises mixing the resulting signal with a firstmixing stage and a second mixing stage; wherein the first mixing stagecomprises a first mixing frequency and a second mixing frequency, thesecond mixing stage comprises a third mixing frequency and a fourthmixing frequency, and the third mixing frequency corresponds to thefirst mixing frequency and the first transmitter frequency, and whereinthe second mixing frequency is in quadrature with the first mixingfrequency, and the fourth mixing frequency is in quadrature with thethird mixing frequency.
 17. A capacitive sensor device comprising: atransmitter electrode; a receiver electrode; a processing systemcommunicatively coupled to the transmitter electrode and the receiverelectrode, the processing system configured to: transmit a firsttransmitter signal with the transmitter electrode, the first transmittersignal comprising a first transmitter frequency; receive a resultingsignal with the receiver electrode, the resulting signal comprisingeffects corresponding to the first transmitter signal; demodulate theresulting signal to produce an upper sideband signal and a lowersideband signal; selectably determine a measurement of a change incapacitive coupling between the transmitter electrode and the receiverelectrode based on at least one of the upper sideband signal and thelower sideband signal; and determine positional information for an inputobject based on the measurement.
 18. The capacitive sensor device ofclaim 17, wherein a measure of interference is determined based on thelower sideband signal when the measurement is determined based on theupper sideband signal, and wherein the measure of interference isdetermined based on the upper sideband signal when the measurement isdetermined based on the lower sideband signal.
 19. The capacitive sensordevice of claim 18, wherein the processing system is configured totransmit a second transmitter signal, different from the firsttransmitter signal, based on the measure of interference.
 20. Thecapacitive sensor device of claim 17, wherein demodulating the resultingsignal to produce the upper sideband signal and the lower sidebandsignal comprises mixing the resulting signal with a first mixing stageand a second mixing stage; wherein the first mixing stage comprises afirst mixing frequency and a second mixing frequency, the second mixingstage comprises a third mixing frequency and a fourth mixing frequency,and the third mixing frequency corresponds to the first mixing frequencyand the first transmitter frequency, and wherein the second mixingfrequency is in quadrature with the first mixing frequency, and thefourth mixing frequency is in quadrature with the third mixingfrequency.